Skeletal muscle is a complex tissue capable increasing its metabolic rate several hundred fold in a matter of seconds. In order to meet energetic demands, skeletal muscle can form ATP through multiple pathways (i.e., PCr hydrolysis, anaerobic glycolysis, and oxidative phosphorylation). Each pathway offers a unique combination of maximal ATP production rate and capacity, and all three must work in concert for effective muscle function. Elucidating the complex integration of these pathways is crucial to the understanding of muscle function in both healthy and diseased states. Although extensive research has been conducted on the regulation and integration of these pathways, several key questions remain unanswered. Part of the reason for this difficulty is due to the techniques used to study skeletal muscle metabolism. For example, many in vitro measurements (e.g., enzyme assays, isolated mitochondria) do not allow the study of integrated muscle function, whereas the use of whole muscle preparations can be confounded by issues such as blood flow and fiber heterogeneity. The isolated fiber technique offers a unique opportunity to study intact skeletal muscle in a controlled environment. Therefore, the isolated fiber technique will be used to: 1.) determine the rate of onset kinetics of glycolysis in different fiber types, 2). determine the role of metabolic channeling in setting the onset kinetics of oxidative phosphorylation, and 3.) determine the intracellular PO2 at which respiration becomes O2 dependent. [unreadable] [unreadable]